Neutrophils play a prominent role in inflammatory conditions, which if uncontrolled, can result in tissue injury. Thus, selective inhibition of a pathway critical for their movement into tissues would be of therapeutic value. In this regard, class I PI3 kinases (PBKs), consisting of a, P, gamma, and delta isoforms, make attractive targets as they play a pivotal role in chemokine-directional migration of these cells. Much research has concentrated on their functions, but progress has been hampered by the lack of inhibitors that 1) are nontoxic so that they may be studied in animal models, and 2) selectively target PDKs that are primarily expressed in leukocytes such as the delta isoform. Utilizing the recently developed small molecule inhibitor of PI3Kdelta, IC87114, and mice deficient in p110delta we provide evidence that this signaling pathway is a valid target for drug development. Oral administration of this compound to mice reduced chemokine-mediated migration and interestingly, adhesive interactions of neutrophils with the vessel wall in a manner analogous to that observed in p110delta null animals. Thus, the purpose of this application is to define the biological role of PI3Kdelta in neutrophil localization at sites of inflammation and its ability to modulate the proinflammatory state of cytokine-stimulated endothelium. Our studies will be directed at three specific aims. In Aim 1, we will evaluate the role of PI3Kdelta in promoting neutrophil accumulation in inflamed lung and joints using murine models that replicate disease states in man. In Aim 2, we will determine the importance of this isoform relative to PI3K/gamma and the p38MAPK signaling pathways in promoting neutrophil activation and migration in response to endogenous vs. bacteria-derived chemoattractants in vitro and in vivo. The latter will be accomplished by direct visualization of the behavior of GFP-expressing cells using intravital microscopy. In Aim 3, we will determine whether class la and Ib PBKs exist in functional complexes in endothelium and explore the mechanism(s) by which they participate in the ability of this cell type to recruit neutrophils. Together, these studies will determine the importance of PI3Kdelta in neutrophil recruitment in inflammation as well as provide insight into therapeutic strategies designed to limit their migration into tissues. Moreover, our results will define a new role for class I PBKs, regulation of the adhesive properties of inflamed endothelium.